1. Field of the Invention
The invention relates to a tungsten metal removing solution which is effective for removing unnecessary tungsten metal causing a film formation on a semiconductor substrate, etc., or adhering to them, more particularly, relates to a tungsten metal removing solution, which has little causticity toward silicon in the substrate back side and titanium nitride or silicon oxide of the liner, and a method for removing tungsten metal using by use thereof.
2. Description of Related Art
An example is reported in which tungsten silicide or almost tungsten metal which is made by heat treatment of tungsten silicide is used as a gate electrode material (for example, JP A 62-143422), and use of titanium tungsten or titanium aluminum alloys as a wiring material for semiconductors is reported (for example, JP A 8-250462). In addition, tungsten metal has been used as a metal for filling contact holes or via holes according to a multiplelayer trend in a semiconductor substrate, and further, a case is reported in which after filling contact holes or via holes with tungsten metal, tungsten metal causing a film formation on a substrate front side is processed and used as wiring.
In recent years, tungsten metal has been used as an electrode material in DRAM, FeRAM, System LSI, etc. Although there are methods such as sputtering or CVD as a method to cause a film formation of tungsten metal, in any method whatever, tungsten metal causes the film formation on the total surface of a substrate including its periphery. Tungsten metal, which causes a film formation on a periphery and back side of the substrate except a device forming area or adheres to them, is spontaneously separable easily, and it is considered that the separated tungsten metal adheres to the device forming area and induces a cross contamination of a film forming apparatus through a conveyor system, therefore, before moving to the next step, the complete removing of tungsten metal, which causes a film formation on the periphery and back side of the substrate except a device forming area or adheres to them, is examined. Here, “areas except a device forming area” means areas including not only the facet and back side of a semiconductor substrate, but the periphery of a device forming surface.
Although there is so far no report of a removing solution for removing tungsten metal which causes a film formation on a periphery or back side of the substrate except a device forming area or adheres to them, an etching fluid for tungsten metal or tungsten alloy has been reported.
For example, although mix fluids (JP A 8-250462, JP A 11-219946, JP A 2000-311891) of ammonia and water with hydrogen peroxide or hydrogen peroxide water are proposed as etching fluids for tungsten metal, there are problems that hydrogen peroxide water easily decomposes generating oxygen and the life time as the etching fluid is short. Further, it can not necessarily be said that these etching fluids are practical etching fluids due to production of granular or membranous residues after etching, and the like. Therefore, these are not appropriate as the removing solution for tungsten metal.
In addition, in the production of semiconductor or devices, a silicon oxide insulating film and a tungsten metal film make a stacked state on the facet or back side of a silicon substrate, though a step to remove the tungsten metal film and a step to remove silicon oxide are carried out in the same apparatus, and the removing of silicon oxide film is carried out using usually an acidic reagent fluid such as hydrofluoric acid. Therefore, when the removing of tungsten metal film is carried out using a basic reagent fluid such as ammonia, there is a problem that a salt such as ammonium fluoride is deposited in an etching room or an exhaust duct.
Although an aqueous solution containing hydrofluoric acid and nitric acid may be considered as an acidic tungsten removing solution to prevent deposition of salts, this aqueous solution corrodes silicon as well as silicon oxide, and therefore, it is reported that it is not appropriate in a device production (JP A 8-250462).
On the other hand, although a targeted metal for removing is different, a composition containing orthoperiodic acid and nitric acid is reported as an acidic removing solution to remove ruthenium metal which causes a film formation on the periphery of a semiconductor substrate and adheres to it (JP A 2001-68463). However, the removing of tungsten metal is not disclosed in any way.
In addition, although a removing solution composition containing orthoperiodic acid, hydrofluoric acid and sulfuric acid is reported (U.S. Pat. No. 6,461,978), a removing solution composition which does not contain sulfuric acid as an essential component is silent in this document.